5′-non-transcribed flanking region and 5′-untranslated region play distinctive roles in sulfur deficiency induced expression of SULFATE TRANSPORTER 1;2 in Arabidopsis roots

Plants increase sulfate uptake activity under sulfur deficiency (？S). In Arabidopsis, SULTR1;2 is the major high-affinity sulfate transporter induced in epidermis and cortex of roots for mediating sulfate uptake under ？S. Though it is known that transcript levels of SULTR1;2 increase under ？S largely due to the function of 5′-upstream region, contributions of 5′-non-transcribed flanking region and 5′-untranslated region (UTR) to transcriptional and post-transcriptional regulations have not yet been individually verified. To investigate the roles of 5′UTR of SULTR1;2 in ？S responses, transcript levels and activities of firefly luciferase (Luc) were analyzed in transgenic plants expressing Luc under the control of the 2,160-bp long 5′-upstream region of SULTR1;2 with (PL2160) or without (PL2160ΔUTR) the 154-bp 5′UTR. Both transgenic plants expressed similar levels of Luc mRNAs that showed significant accumulations under ？S relative to +S regardless of presence of the 5′UTR. In contrast, Luc activities were detected only in PL2160 plants, suggesting presence of 5′UTR of SULTR1;2 being necessary for translational initiation while its absence impairing translation of functional Luc protein in PL2160ΔUTR. These results indicate an essential role of the 5′-non-transcribed flanking region of SULTR1;2 at positions ？2160 to ？155 in ？S-responsive transcriptional regulation